This invention relates to an apparatus and method for solution mining a subterranean deposit of soluble minerals. More particularly, this invention relates to an apparatus and method whereby a subterranean cavity containing a rubble pile within a cavity in the deposit is mined.
Subterranean deposits of minerals such as sodium chloride, potassium chloride, magnesium chloride, trona, limestone, mixtures thereof and the like are solution mined by solubilizing the deposits with a suitable solvent and withdrawing from the deposit an enriched solution from which the minerals can be produced. Consequently, large cavities are created where the minerals have been vacated. Frequently, these cavities become so large that the roofs thereof collapse, thereby creating a rubble pile containing soluble and insoluble minerals. It may be desirable to recover a portion of the rubbilized desirable soluble minerals which may be in co-existence with other soluble minerals as well as the insolubles. Unfortunately, unless a conduit penetrates the rubble, it is difficult to mine because the desirable minerals are buried beneath insolubles and undesirable soluble minerals, resulting in a small surface area of the desirable mineral exposed to the action of unsaturated solvent.
In some cases the rubble pile will be intentionally created to increase the exposed surface area of the desired mineral. But, after mining for some time, the rubble pile becomes impermeable to the solvent owing to an accumulation of insolubles and/or owing to an increased ratio of an undesirable soluble mineral present.
It is therefore desirable to penetrate the rubble pile with a liner or tubing to introduce solvent into the rubble pile and dissolve the desired mineral content therein or to withdraw enriched solution from within the rubble pile. Because of the difficulty in drilling a hole in the rubble pile and subsequently setting a liner therein owing to the drilled hole caving in and owing to the hole being a small target at great depths, a drill down liner and wash down liner have been introduced to the art in U.S. Pat. Nos. 3,600,039 and 3,556,597 respectively.
The drill down liner of U.S. Pat. No. 3,600,039 allows the liner to be set along with packers which seal the annular space between the casing and the liner. Thrust bearings at the ends of the liner allow drilling to take place without the liner also turning, thereby reducing the amount of damage to the liner and packers. However, the drilling string does experience axial force which sometimes unavoidably causes damage to the packers. Also, the drill string must be removed to allow a large volume to be withdrawn. This removal operation is very cumbersome.
The wash down liner of U.S. Pat. No. 3,556,597 works well only when it does not encounter insoluble material of sufficient size which blocks its progress. It is also blocked if it encounters junk pipe left in the rubble pile by previous operations. This junk pipe includes casings intentionally cut or liners or tubing which have broken off by roof cavings. The wash down liners are a cheap, easy, quick way to re-establish a return system when a cavity contains rubble composed of soluble material, but as the cavity becomes older, it fails owing to caving of insoluble roof material or owing to an excess of junk pipe in its path.